pthread barriers with spinning

7e161483 · Nickolai Zeldovich · b9d32b50 · 7e161483 · 7e161483
--- a/include/pthread.h
+++ b/include/pthread.h
+#pragma once
+
 /*
 * Our minimal version of pthreads
 */

+#include "atomic.hh"
+
 typedef int pthread_t;
 typedef int pthread_attr_t;
 typedef int pthread_key_t;
+typedef int pthread_barrierattr_t;
+typedef std::atomic<unsigned> pthread_barrier_t;

-int       pthread_create(pthread_t* tid, const pthread_attr_t* attr, void* (*start)(void*), void* arg);
+int       pthread_create(pthread_t* tid, const pthread_attr_t* attr,
+                         void* (*start)(void*), void* arg);
 pthread_t pthread_self(void);

 int       pthread_key_create(pthread_key_t* key, void (*destructor)(void*));
 void*     pthread_getspecific(pthread_key_t key);
 int       pthread_setspecific(pthread_key_t key, void* value);
+
+int       pthread_barrier_init(pthread_barrier_t *b,
+                               const pthread_barrierattr_t *attr,
+                               unsigned count);
+int       pthread_barrier_wait(pthread_barrier_t *b);
--- a/lib/threads.cc
+++ b/lib/threads.cc
@@ -58,3 +58,20 @@ pthread_setspecific(pthread_key_t key, void* value)
  __asm volatile("movq %0, %%fs:(%1)" : : "r" (value), "r" (key * 8));
  return 0;
 }
+
+int
+pthread_barrier_init(pthread_barrier_t *b,
+                     const pthread_barrierattr_t *attr, unsigned count)
+{
+  b->store(count);
+  return 0;
+}
+
+int
+pthread_barrier_wait(pthread_barrier_t *b)
+{
+  (*b)--;
+  while (*b != 0)
+    ;   // spin
+  return 0;
+}